1. Field of the Invention
The present invention relates to a laser processing device.
2. Description of Related Art
Conventionally, as laser processing apparatus of this type, there have been known those which perform thermal processing, such as cutting, welding and heating, by radiating a laser beam on the surface of a workpiece. As an example, reference is here made to the apparatus shown in FIG. 6.
The reflection mirror 53 is for changing the travelling direction of a laser beam 52 emitted from a laser beam generator 51. And, the laser beam reflected by the reflection mirror 53 is incident on a processing head 54.
A workpiece 55 is disposed just under the processing head 54 and in a fixed state to a moving device 56. The moving device 56 is moved while the laser beam 52 is radiated onto the workpiece 55, whereby a spot of the laser beam 52 formed on the workpiece 55 moves in a relative manner. In this way, a predetermined thermal processing is applied to the workpiece 55 using the laser beam 52.
As an example of such thermal processing, cutting work will be explained below. As shown in FIG. 7, the condenser lens 57 is disposed fixedly in the interior of the processing head 58. The laser beam 52 which is incident on the processing head 58 passes through the condenser lens 57 while being converged by the same lens. Then the workpiece 55 is melted in the position of the focus point 59 of the laser beam 52. As a result, the portion of the workpiece 55 melted as molten metal 60 by the laser beam 52 is blown off by the strong stream of the processing gas 61 which is active gas, e.g., oxygen gas, to form cut slot 62 in the workpiece 55.
In welding work, the laser beam needs to have a higher power output than the laser beam used in the cutting work. Therefore, a parabolic mirror which has a high strength under high-light or high-heat conditions, as compared with the condenser lens, is conventionally used. As shown in FIG. 8, a plane reflective mirror 63 and the parabolic mirror 64 which is disposed opposite to the plane reflective mirror 63 are disposed fixedly in the interior of the processing head 65. The laser beam 52 incident on the processing head 65 is reflected from the plane reflective mirror 63 and is incident on the parabolic mirror 64. After the travelling direction of the laser beam 52 is changed by the parabolic mirror 64, the laser beam 52 is converged and the converged laser beam 52 is radiated on the workpiece 55. Then, the workpiece 55 is melted in the position of the focus point 66 of the laser beam 52. At the same time, the processing gas 68 which is inert gas, e.g., argon gas, is applied weakly to the workpiece 55. As a result, the portion of the workpiece 5 melted as molten metal 67 by the laser beam 52 is covered with a weak stream of the processing gas 68, and again solidifies while the oxidation thereof is prevented.
On the other hand, in heating work, such as hardening, it is required that the energy of a laser beam is distributed uniformly. Therefore, as shown in FIG. 9, a kaleidoscope 70 is disposed fixedly in the interior of the processing head 71. The laser beam 52 which is incident on the processing head 71 passes through the condenser lens 72 while being converged by the same lens. The converged laser beam 52 is incident on the kaleidoscope 70. The laser beam 52 is made to be in multiple reflection inside of the kaleidoscope 70, so that the energy distribution of the laser beam 52 becomes uniform. The laser beam 52 is radiated on the workpiece 55 after passing through the condenser lens 73. A laser beam absorbent 74 of a graphite type is coated on the surface of the workpiece 55 in order to absorb the laser beam 52 efficiently. After the workpiece 55 is rapidly heated by the radiated laser beam 52 so as to reach a hardening temperature, the workpiece 55 is rapidly cooled owing to the its heat conduction. As a result, the laser beam 52 forms a hardened portion 75 in the workpiece 55.
Thus, it is desirable to use the processing head having optical elements, such as a condenser lens, a parabolic mirror or kaleidoscope, according to the type of a thermal processing to be done. Also, if the laser processing apparatus is to perform one type of thermal processing, it is desirable to select the processing head having the optimum optical elements according to the processing conditions desired.
However, in the conventional laser processing apparatus, the processing head is semifixed or detachably fixed. Therefore, in the case of performing different types of thermal processing in such a conventional laser processing apparatus, it is necessary to change processing heads from one to another appropriately according to the type of the thermal processing to be done. In the conventional laser processing apparatus, this processing head changing operation is conducted manually, thus causing the problem of lowering production efficiency.
A known type of laser processing apparatus capable of solving the above-mentioned problem is shown in Fig. 10. The laser processing apparatus includes a frame 102, and further includes a processing head for welding work 106, a processing head for cutting work 105 and a processing head for hardening work 107, which are disposed fixedly to the frame 102 through a holder 119. Moreover, the laser processing apparatus includes a plane reflective mirror 104 which can move in order to introduce a laser beam 103 emitted from a laser beam generator 101 into the one of the three processing heads 106, 105 and 107. That is, according to the laser processing apparatus, an optimum processing head can be selected from the three processing heads 106, 105 and 107 by moving the reflective mirror 104. And, a desired thermal processing can be performed by moving a workpiece 126. The workpiece 126 is moved by a moving device 127 having a first direction feeding device 130 and a second direction feeding device 140. Therefore, there is no need to change the processing heads from one to another appropriately according to the type of the thermal processing to be done.
However, in the above-mentioned laser processing apparatus, the three processing heads 106, 105 and 107 are disposed fixedly to the frame 102. Therefore, it is necessary to provide a large space where the moving device 127 can move the workpiece, because the moving device 127 needs to move toward three positions corresponding to each processing heads 106, 105 and 107, and further to move within a processing range for processing the workpiece 126 by each processing head. For instance, as shown in the left side of FIG. 10, the moving device 127 has to be able to move to a position shown by the dotted line. Therefore, there is a problem that the size of the laser processing apparatus is increased.